Disaster recovery at high reliability in a storage cluster

ABSTRACT

A storage grid is provided. The storage grid includes a first cluster, a second cluster, and a third cluster. Each of the first cluster, the second cluster and the third cluster is configured to store an amount of data ranging from a portion of a copy of the data to a full copy of the data. The first cluster has a full copy of data written to the first cluster and at least a partial copy of data written to the second and third cluster. The second cluster has a full copy of data written to the second cluster, and at least a partial copy of the data written to the first and third cluster. The third cluster has a full copy of data written to the third cluster and at least a partial copy of the data written to the first and second cluster. A method of storing data is also provided.

BACKGROUND

Solid-state memory, such as flash, is currently in use in solid-statedrives (SSD) to augment or replace conventional hard disk drives (HDD),writable CD (compact disk) or writable DVD (digital versatile disk)drives, collectively known as spinning media, and tape drives, forstorage of large amounts of data. Flash and other solid-state memorieshave characteristics that differ from spinning media. Yet, manysolid-state drives are designed to conform to hard disk drive standardsfor compatibility reasons, which makes it difficult to provide enhancedfeatures or take advantage of unique aspects of flash and othersolid-state memory. Storage systems, whether applying solid-state memorysuch as flash, or hard disk drives, or hybrid combinations of the two,are vulnerable to disasters such as multiple component failures, systempower loss, data theft and physical theft (i.e., loss of both componentsand data). In addition, conventional storage architectures may allow forexposure of the data in the case of physical theft of a storage module.

It is within this context that the embodiments arise.

SUMMARY

In some embodiments, a storage grid is provided. The storage gridincludes a first cluster, a second cluster, and a third cluster. Each ofthe first cluster, the second cluster and the third cluster isconfigured to store an amount of data ranging from a portion of a copyof the data to a full copy of the data. The first cluster has a fullcopy of data written to the first cluster and at least a partial copy ofdata written to the second and third cluster. The second cluster has afull copy of data written to the second cluster, and at least a partialcopy of the data written to the first and third cluster. The thirdcluster has a full copy of data written to the third cluster and atleast a partial copy of the data written to the first and secondcluster.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings. These drawings in no waylimit any changes in form and detail that may be made to the describedembodiments by one skilled in the art without departing from the spiritand scope of the described embodiments.

FIG. 1 is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2 is a system diagram of an enterprise computing system, which canuse one or more of the storage clusters of FIG. 1 as a storage resourcein some embodiments.

FIG. 3 is a block diagram showing multiple storage nodes andnon-volatile solid state storage with differing capacities, suitable foruse in the storage cluster of FIG. 1 in accordance with someembodiments.

FIG. 4 is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 5 is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIGS. 6A-C are block diagrams illustrating a storage grid, which couldinclude storage units having solid-state memory, or other types ofstorage, splitting a copy of data in various proportions, in accordancewith some embodiments.

FIG. 7 is a block diagram of a mechanism for shared secrets, which canbe utilized by the storage clusters of FIGS. 6A-C in accordance withsome embodiments.

FIG. 8 is a flow diagram of a method of storing data in a storage grid,which can be practiced on or by embodiments of the storage clusters inaccordance with some embodiments.

FIG. 9 is an illustration showing an exemplary computing device whichmay implement the embodiments described herein.

DETAILED DESCRIPTION

The embodiments below describe a storage grid. The storage grid includesstorage clusters and each of the storage clusters may includenon-volatile solid state storage units that are arranged forsurvivability and decreased vulnerability. The storage clusters are notlimited to the use of non-volatile solid state storage as any suitablestorage class medium including volatile storage, non-volatile storage,solid state storage, disk drives, or any combinations of storage classmedium, may be integrated into the storage clusters. In one arrangement,three storage clusters are provided in the storage grid with eachstorage cluster storing a full copy of data or a portion of the data.After a period of time and multiple data writes, e.g., in asteady-state, no one storage cluster has a copy of all of the data thathas been written to the storage clusters of the storage grid. Thus, thesystem is not vulnerable to theft of any one storage cluster or anunrecoverable loss of any one storage cluster of the storage grid. Anytwo of the storage clusters in combination can recover all of the datathat has been written to the storage grid so that the system is able tosurvive a failure of any one of the storage clusters. That is, thereexists two full copies of the data are distributed within the storagegrid. Two storage clusters of the storage grid can always recreate thedata either by any one of the storage clusters having a full copy of thedata or by two of the storage clusters having portions of the dataarranged so that the recovery of the portions of the data yields thefull copy of the data. The embodiments are not limited to three storageclusters within a storage grid as three or more independent storageclusters may be coupled together as a storage grid. In addition, theportions of the copy of the data may be distributed over two or morestorage clusters.

The storage clusters store user data, such as user data originating fromone or more user or client systems or other sources external to thestorage cluster. The storage cluster distributes user data acrossstorage nodes housed within a chassis, using erasure coding andredundant copies of metadata. Erasure coding refers to a method of dataprotection or reconstruction in which data is stored across a set ofdifferent locations, such as disks, storage nodes or geographiclocations. Flash memory is one type of solid-state memory that may beintegrated with the embodiments, although the embodiments may beextended to other types of solid-state memory or other storage medium,including non-solid state memory. Control of storage locations andworkloads are distributed across the storage locations in a clusteredpeer-to-peer system. Tasks such as mediating communications between thevarious storage nodes, detecting when a storage node has becomeunavailable, and balancing I/Os (inputs and outputs) across the variousstorage nodes, are all handled on a distributed basis. Data is laid outor distributed across multiple storage nodes in data fragments orstripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server.

The storage cluster is contained within a chassis, i.e., an enclosurehousing one or more storage nodes. A mechanism to provide power to eachstorage node, such as a power distribution bus, and a communicationmechanism, such as a communication bus that enables communicationbetween the storage nodes are included within the chassis. The storagecluster can run as an independent system in one location according tosome embodiments. In one embodiment, a chassis contains at least twoinstances of both the power distribution and the communication bus whichmay be enabled or disabled independently. The internal communication busmay be an Ethernet bus, however, other technologies such as PeripheralComponent Interconnect (PCI) Express, InfiniBand, and others, areequally suitable. The chassis provides a port for an externalcommunication bus for enabling communication between multiple chassis,directly or through a switch, and with client systems. The externalcommunication may use a technology such as Ethernet, InfiniBand, FibreChannel, etc. In some embodiments, the external communication bus usesdifferent communication bus technologies for inter-chassis and clientcommunication. If a switch is deployed within or between chassis, theswitch may act as a translation between multiple protocols ortechnologies. When multiple chassis are connected to define a storagecluster, the storage cluster may be accessed by a client using eitherproprietary interfaces or standard interfaces such as network filesystem (NFS), common internet file system (CIFS), small computer systeminterface (SCSI) or hypertext transfer protocol (HTTP). Translation fromthe client protocol may occur at the switch, chassis externalcommunication bus or within each storage node.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units. One embodimentincludes a single storage server in each storage node and between one toeight non-volatile solid state memory units, however this one example isnot meant to be limiting. The storage server may include a processor,dynamic random access memory (DRAM) and interfaces for the internalcommunication bus and power distribution for each of the power buses.Inside the storage node, the interfaces and storage unit share acommunication bus, e.g., PCI Express, in some embodiments. Thenon-volatile solid state memory units may directly access the internalcommunication bus interface through a storage node communication bus, orrequest the storage node to access the bus interface. The non-volatilesolid state memory unit contains an embedded central processing unit(CPU), solid state storage controller, and a quantity of solid statemass storage, e.g., between 2-32 terabytes (TB) in some embodiments. Anembedded volatile storage medium, such as DRAM, and an energy reserveapparatus are included in the non-volatile solid state memory unit. Insome embodiments, the energy reserve apparatus is a capacitor,super-capacitor, or battery that enables transferring a subset of DRAMcontents to a stable storage medium in the case of power loss. In someembodiments, the non-volatile solid state memory unit is constructedwith a storage class memory, such as phase change or magnetoresistiverandom access memory (MRAM) that substitutes for DRAM and enables areduced power hold-up apparatus.

FIG. 1 is a perspective view of a storage cluster 160, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 160, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 160 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 160 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in FIG. 1, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 158populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

FIG. 2 is a system diagram of an enterprise computing system 102, whichcan use one or more of the storage nodes, storage clusters and/ornon-volatile solid state storage of FIG. 1 as a storage resource 108.For example, flash storage 128 of FIG. 2 may integrate the storagenodes, storage clusters and/or non-volatile solid state storage of FIG.1 in some embodiments. The enterprise computing system 102 hasprocessing resources 104, networking resources 106 and storage resources108, including flash storage 128. A flash controller 130 and flashmemory 132 are included in the flash storage 128. In variousembodiments, the flash storage 128 could include one or more storagenodes or storage clusters, with the flash controller 130 including theCPUs, and the flash memory 132 including the non-volatile solid statestorage of the storage nodes. In some embodiments flash memory 132 mayinclude different types of flash memory or the same type of flashmemory. The enterprise computing system 102 illustrates an environmentsuitable for deployment of the flash storage 128, although the flashstorage 128 could be used in other computing systems or devices, largeror smaller, or in variations of the enterprise computing system 102,with fewer or additional resources. The enterprise computing system 102can be coupled to a network 140, such as the Internet, in order toprovide or make use of services. For example, the enterprise computingsystem 102 could provide cloud services, physical computing resources,or virtual computing services.

In the enterprise computing system 102, various resources are arrangedand managed by various controllers. A processing controller 110 managesthe processing resources 104, which include processors 116 andrandom-access memory (RAM) 118. Networking controller 112 manages thenetworking resources 106, which include routers 120, switches 122, andservers 124. A storage controller 114 manages storage resources 108,which include hard drives 126 and flash storage 128. Other types ofprocessing resources, networking resources, and storage resources couldbe included with the embodiments. In some embodiments, the flash storage128 completely replaces the hard drives 126. The enterprise computingsystem 102 can provide or allocate the various resources as physicalcomputing resources, or in variations, as virtual computing resourcessupported by physical computing resources. For example, the variousresources could be implemented using one or more servers executingsoftware. Files or data objects, or other forms of data, are stored inthe storage resources 108.

In various embodiments, an enterprise computing system 102 could includemultiple racks populated by storage clusters, and these could be locatedin a single physical location such as in a cluster or a server farm. Inother embodiments the multiple racks could be located at multiplephysical locations such as in various cities, states or countries,connected by a network. Each of the racks, each of the storage clusters,each of the storage nodes, and each of the non-volatile solid statestorage could be individually configured with a respective amount ofstorage space, which is then reconfigurable independently of the others.Storage capacity can thus be flexibly added, upgraded, subtracted,recovered and/or reconfigured at each of the non-volatile solid statestorages. As mentioned previously, each storage node could implement oneor more servers in some embodiments.

FIG. 3 is a block diagram showing multiple storage nodes 150 andnon-volatile solid state storage 152 with differing capacities, suitablefor use in the chassis of FIG. 1. Each storage node 150 can have one ormore units of non-volatile solid state storage 152. Each non-volatilesolid state storage 152 may include differing capacity from othernon-volatile solid state storage 152 on a storage node 150 or in otherstorage nodes 150 in some embodiments. Alternatively, all of thenon-volatile solid state storages 152 on a storage node or on multiplestorage nodes can have the same capacity or combinations of the sameand/or differing capacities. This flexibility is illustrated in FIG. 3,which shows an example of one storage node 150 having mixed non-volatilesolid state storage 152 of four, eight and thirty-two TB capacity,another storage node 150 having non-volatile solid state storage 152each of thirty-two TB capacity, and still another storage node havingnon-volatile solid state storage 152 each of eight TB capacity. Variousfurther combinations and capacities are readily devised in accordancewith the teachings herein. In the context of clustering, e.g.,clustering storage to form a storage cluster, a storage node can be orinclude a non-volatile solid state storage 152. Non-volatile solid statestorage 152 is a convenient clustering point as the non-volatile solidstate storage 152 may include a nonvolatile random access memory (NVRAM)component, as will be further described below.

Referring to FIGS. 1 and 3, storage cluster 160 is scalable, meaningthat storage capacity with non-uniform storage sizes is readily added,as described above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 4 is a block diagram showing a communications interconnect 170 andpower distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 1, the communications interconnect 170 can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 160 occupy a rack, thecommunications interconnect 170 can be included in or implemented with atop of rack switch, in some embodiments. As illustrated in FIG. 4,storage cluster 160 is enclosed within a single chassis 138. Externalport 176 is coupled to storage nodes 150 through communicationsinterconnect 170, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 3. In addition, one or more storage nodes 150 may be acompute only storage node as illustrated in FIG. 4. Authorities 168 areimplemented on the non-volatile solid state storages 152, for example aslists or other data structures stored in memory. In some embodiments theauthorities are stored within the non-volatile solid state storage 152and supported by software executing on a controller or other processorof the non-volatile solid state storage 152. In a further embodiment,authorities 168 are implemented on the storage nodes 150, for example aslists or other data structures stored in the memory 154 and supported bysoftware executing on the CPU 156 of the storage node 150. Authorities168 control how and where data is stored in the non-volatile solid statestorages 152 in some embodiments. This control assists in determiningwhich type of erasure coding scheme is applied to the data, and whichstorage nodes 150 have which portions of the data. Each authority 168may be assigned to a non-volatile solid state storage 152. Eachauthority may control a range of inode numbers, segment numbers, orother data identifiers which are assigned to data by a file system, bythe storage nodes 150, or by the non-volatile solid state storage 152,in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 1-4, two of the many tasks of the CPU 156 on astorage node 150 are to break up write data, and reassemble read data.When the system has determined that data is to be written, the authority168 for that data is located as above. When the segment ID for data isalready determined the request to write is forwarded to the non-volatilesolid state storage 152 currently determined to be the host of theauthority 168 determined from the segment. The host CPU 156 of thestorage node 150, on which the non-volatile solid state storage 152 andcorresponding authority 168 reside, then breaks up or shards the dataand transmits the data out to various non-volatile solid state storage152. The transmitted data is written as a data stripe in accordance withan erasure coding scheme. In some embodiments, data is requested to bepulled, and in other embodiments, data is pushed. In reverse, when datais read, the authority 168 for the segment ID containing the data islocated as described above. The host CPU 156 of the storage node 150 onwhich the non-volatile solid state storage 152 and correspondingauthority 168 reside requests the data from the non-volatile solid statestorage and corresponding storage nodes pointed to by the authority. Insome embodiments the data is read from flash storage as a data stripe.The host CPU 156 of storage node 150 then reassembles the read data,correcting any errors (if present) according to the appropriate erasurecoding scheme, and forwards the reassembled data to the network. Infurther embodiments, some or all of these tasks can be handled in thenon-volatile solid state storage 152. In some embodiments, the segmenthost requests the data be sent to storage node 150 by requesting pagesfrom storage and then sending the data to the storage node making theoriginal request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain metadata, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIG. 5) in accordance with an erasure coding scheme. Usage of the termsegments refers to the container and its place in the address space ofsegments in some embodiments. Usage of the term stripe refers to thesame set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top is the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage 152 may be assigned a range of address space. Withinthis assigned range, the non-volatile solid state storage 152 is able toallocate addresses without synchronization with other non-volatile solidstate storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (LDPC) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudorandomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(RUSH) family of hashes, including Controlled Replication Under ScalableHashing (CRUSH). In some embodiments, pseudo-random assignment isutilized only for assigning authorities to nodes because the set ofnodes can change. The set of authorities cannot change so any subjectivefunction may be applied in these embodiments. Some placement schemesautomatically place authorities on storage nodes, while other placementschemes rely on an explicit mapping of authorities to storage nodes. Insome embodiments, a pseudorandom scheme is utilized to map from eachauthority to a set of candidate authority owners. A pseudorandom datadistribution function related to CRUSH may assign authorities to storagenodes and create a list of where the authorities are assigned. Eachstorage node has a copy of the pseudorandom data distribution function,and can arrive at the same calculation for distributing, and laterfinding or locating an authority. Each of the pseudorandom schemesrequires the reachable set of storage nodes as input in some embodimentsin order to conclude the same target nodes. Once an entity has beenplaced in an authority, the entity may be stored on physical devices sothat no expected failure will lead to unexpected data loss. In someembodiments, rebalancing algorithms attempt to store the copies of allentities within an authority in the same layout and on the same set ofmachines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing an Ethernet backplane, and chassis are connected together to forma storage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed matching). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being replicated.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 5 is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (NIC) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 5, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (NVRAM)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 5, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (PLD) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

FIGS. 6A-C are block diagrams illustrating a storage grid 671 splittinga copy of data in various proportions, in accordance with someembodiments. Storage clusters 160A, 160B, and 160C are depicted in threerelated scenarios as members of the storage grid 671. Embodimentsdepicted in FIGS. 6A-C, and variations thereof, demonstratesurvivability of data and storage under failure or theft of one of thestorage clusters 160A, 160B, 160C. The three storage clusters 160A,160B, 160C, are positioned around a region 672 or other defined area.The region 672 could be a city, a data center, a campus with differingfailure domains 672A, 672B, and 672C or some other defined area in someembodiments. Each of the storage clusters within the storage grid isseparated from each other storage cluster by a portion of a width of theregion 672 or other defined area, and/or by differences in the failuredomains, e.g., each of the storage clusters has separate power systems.The geographical separation of storage clusters 160A, 160B, and 160Cprovides a measure of protection against physical disasters such as anexplosion, a building collapse, local flooding, a fire, and so on. Suchseparations are by example only, and other separations are possible. Themaximum separation between storage clusters 160A, 160B, and 160C may berelated to a specified time delay in a network, so that delays are notexcessive.

When data arrives at storage cluster 160A, the data is stored, andcopies of portions of the data are stored at additional storageclusters. For example, a fractional portion of the data stored instorage cluster 160A is sent to storage cluster 160B and the remainingcomplementary fractional portion of the data is sent to storage cluster160C. A similar sequence is followed when data arrives at either of theother two storage clusters 160B or 160C as illustrated in FIGS. 6B and6C, respectively. In some embodiments, the storage grid may determine todistribute the portions of the data stored at storage clusters 160B and160C non-equally based on external factors such as performance,available storage space, or some other reason. Over time with many datawrites, data becomes distributed among the three storage clusters 160A,160B, and 160C in such a manner that no one storage cluster 160A, 160B,160C has all of the data. However, the data can be read from, recoveredor reconstructed from any two of the storage clusters 160A, 160B, 160C.In some embodiments the recovery of the data is performed byinterleaving the recovered data portions from alternating storageclusters.

In the scenario of FIG. 6A, data 676 arrives at the storage cluster160A, which stores a copy of the data. Storage cluster 160A thenforwards a portion 676A of a copy of the data 676 to the storage cluster160C for storage. Storage cluster 160A also forwards the remainingcomplementary portion 676B of the data 676 to storage cluster 160B forstorage. In the scenario of FIGS. 6B and 6C a similar methodology isfollowed where a first storage cluster retains a copy of the receiveddata and then forwards a portion of the data and the complementaryremaining portion of the data to a second and third storage cluster.Thus, after the operations depicted in the FIGS. 6A-C occur, the firststorage cluster 160A has a full copy of the first data 676, a copy of aportion 678A of the second data 678, and a copy of a portion 680B of thethird data 680. The second storage cluster 160B has a full copy of thesecond data 678, a copy of a portion 676B of the first data 676, and acopy of a portion 680B of the third data 680. The third storage cluster160C has a full copy of the third data 680, a copy of a portion 676A ofthe first data, and a copy of a portion 678B of the second data 678. Inorder to read the first data 676, a read from the first storage cluster160A, or a read of data portions 676B and 676A from the second storagecluster 160B and the third storage cluster 160C, respectively, wouldsuffice. A read of the second data 678 and the third data 680 can beaccomplished in a similar manner through the appropriate storage clusterthat has the full copy of the corresponding data or a combination of thestorage clusters that have the portion and the complementary portion ofthe corresponding data. When data is split and one portion of the datais sent to each of two storage clusters, the two portions of the dataare differing, complementary portions of the data, such that the datacan be reconstructed by combining the two portions of the data together.

The data may be split according to a granularity of a segment, a block,a file, a byte, a word, a bit, or other granularity. In someembodiments, data is split to granularity of one segment, by sendingalternating segments to each of two storage clusters. For example, theentirety of the data may be stored at storage cluster 160A. Then a copyof the data is segmented and a first segment is sent to storage cluster160B, a second segment is sent to storage cluster 160C, a third segmentis sent to storage cluster 160B, a fourth segment is sent to the storagecluster 160C, and so on in an alternating fashion until all the segmentsof the entirety of the data have been distributed. At the end of theoperation, one of the storage clusters 160A has all of the datasegments, and each of the other two storage clusters 160B and 160C has aportion of the data segments. The arrangement for splitting the datacould be fixed throughout the operations, change with each sendingaccording to some algorithm, or change periodically according to someother schedule. The splitting of data could be managed by a portion of anetwork coupling the storage clusters 160A, 160B, 160C, or by thestorage clusters 160A, 160B, 160C themselves. A network could route datato the nearest storage cluster 160A, 160B, 160C. The nearest storagecluster may be determined by estimated network delay on paths to thestorage clusters 160A, 160B, and 160C in some embodiments. Data could berouted in one or both directions around a ring network, or propagatedalong a star network, or routed along any suitable network architecture.Embodiments with more than three storage clusters within a storage gridcould also be devised, with various splits of data among the storageclusters. The three storage clusters 160A-C do not need to be of equalstorage size or storage type.

In some embodiments, the first cluster 160A may be full. In thatinstance, a full copy of the data 676 may be sent to the second cluster160B and another full copy of the data 676 may be sent to the thirdcluster 160C to ensure that at least one full copy can be constructed byany two members of the storage grid 671 (i.e., two of the clusters 160A,160B, 160C) regardless of which cluster 160A, 160B, 160C fails. In otherembodiments a policy may dictate that a full copy of the data 676 isstored on the first cluster 160A, a full copy is stored on the secondcluster 160B, and a full copy is stored on the third cluster 160C forreasons other than efficiency. For example, the policy may be directedtoward accelerating performance for local access.

Still referring to FIGS. 6A-C, two full copies of each data 676, 678,680 are distributed so that two storage clusters can always recreate orrecover the data. The two storage clusters can recreate the data eitherby any one of the storage having a full copy of the data or by two ofthe storage clusters having portions of the data arranged so that whencombined a complete copy of the data is reconstituted. Furtherembodiments can be created by generalizing to systems holding data (m)and redundant data (n), with m+n*2 locations. For example, with m=1,n=1, the total number of systems is three.

It should be appreciated that the above scenarios apply when the storagegrid 671 is operating at full redundancy, or when there is a disaster orother disconnection. There may be periods of time in which one of thestorage clusters 160A, 160B, or 160C is temporarily unreachable and somedata is present only on a single system. The system could temporarilystore full copies of data on the remaining reachable clusters, and notsend data to the unreachable cluster. The system could laterredistribute data per the above descriptions to restore the steady stateonce the unreachable cluster comes back on line or is replaced.

FIG. 7 is a block diagram of a mechanism for shared secrets, which canbe utilized by the storage clusters of FIGS. 6A-C in accordance withsome embodiments. In this embodiment, a shared secret is generated andapplied to encrypt keys used in encrypting and decrypting data stored innon-volatile solid state storage 152. The mechanism for shared secretscan be applied to non-volatile solid state storage 152 in a storagecluster, such as the storage clusters described with reference to FIGS.6A-C. Non-volatile solid state storage 152 are arranged in storageclusters 160, and store encrypted data 798 along with a header 794, inthe embodiment shown in FIG. 7. The header specifies a serial number796, which is unique for each non-volatile solid state storage 152, ashare 790, and an encrypted key 792. The decrypted key (i.e., the keyused for encrypting data, prior to encrypting the key) can be generatedby various mechanisms, for example by a key generation algorithm,executing in the storage unit 152, in a storage node 150, or in thestorage controller 114, or by firmware or hardware therein.

Still referring to FIG. 7, the storage controller 114 has a secretgeneration unit 784, which generates a shared secret according to asecret sharing scheme such as the Shamir, Blakley, or Krawczyk secretsharing schemes, or the Chinese Remainder Theorem. These examples ofsecret sharing schemes are not meant to be limiting or to preclude theuse of other secret sharing schemes. In some embodiments the sharedsecret could include one or more values of constant terms in apolynomial, with the number of shares needed to reconstruct the secretdetermined by the order of the polynomial. In other embodiments,Lagrange basis polynomials are computed from shares in order toreconstruct the master secret. In other embodiments, the number ofshares or storage clusters that are sufficient to recover the mastersecret, which is derived from the shared secret, is one (or anotherpredetermined number) less than the number of storage clusters that aredistributed. With reference to the example arrangement of storageclusters shown in FIG. 6A-C, three shares may distributed (e.g., one toeach of three storage clusters 160A, 160B, 160C). If one storage clusterbecomes unavailable through failure or theft of a storage cluster, thetwo storage clusters remaining are sufficient to recover the mastersecret, from which keys can be decrypted and data decrypted at theremaining storage clusters. In some embodiments, for a given storagecluster, decrypting the encrypted key applies a device-specific value,such as the serial number 796 of the non-volatile solid state storage152.

Continuing with FIG. 7, the master secret module 786 coordinates withthe share generation unit 782, which generates shares 790 of the sharedsecret. Further, the master secret module 786 coordinates with the keyencryption unit 788, to produce encrypted keys 792 from the decryptedkey for each storage unit 152, by application of the shared secret. Eachtime data is written to a storage unit 152, the header 794 includes theappropriate share 790 and encrypted key 792, as distributed by theshared generation unit 782 and the key encryption unit 788,respectively. In this manner data could be encrypted at each of thestorage clusters in FIGS. 6A-C. Theft of any one of the storage clusterswould not reveal the master secret or allow decryption of the keys.Failure at any one of the storage clusters could still be followed byrecovery of the master secret from the remaining storage clusters. Inthis context, all storage clusters are able to participate in theprocessing of stored data, and, if a failure occurs, two of the storageclusters have sufficient content to re-create 100% of the data as wellas 100% of the decryption key.

In some cases there may be an additional key added externally to one ormore of the storage clusters. This additional key is used to enableexternal data access through that storage cluster. The additional keymay be in the form of a password, physical token or other mechanism.This allows the local storage cluster to be placed in a distrustedenvironment without concerns about unauthorized access through thatcluster. In some cases the additional physical and/or logical key may bepresent in a trusted environment. The key may be removed by a user todisable external access to data through that storage cluster withoutshutting down functionality of the storage grid. A user may at a latertime add back a key or token to the system to re-authorize data accessthrough that storage cluster.

In one embodiment, storage clusters allow external connectivity tothemselves using identical addresses (e.g., identical IP addresses), inorder to provide the capability of offering locally accessible storageusing one global network address. In this embodiment, clients choosewhich physical path to take to communicate to the closest storagecluster by sending traffic to the network and the network routers senddata packets to the closest storage cluster using routing techniquessuch as OSPF (Open Shortest Path First) routes or BGP (Border GatewayProtocol) health injection routes. In further examples, the networkinterfaces for each of the storage clusters of the storage grid may becompletely different from each other, and hosts could connect to each ofthe storage clusters by unique addresses bound to each storage cluster.

FIG. 8 is a flow diagram of a method of storing data in a storage grid.The method may be practiced with other types of storage beside solidstate storage. Many of the actions described in the method can beperformed by one or more processors. In an action 802, data is receivedfor writing. For example, a storage cluster that is one of the threestorage clusters in the arrangement depicted in FIG. 6A-C could receivedata from the network for writing to the storage cluster. In an action804, the data is stored at one of the storage clusters. This could bethe storage cluster that received the data, or the data could be passedto another one of the storage clusters and written to that storagecluster.

In an action 806 of FIG. 8, a fraction or portion of the data is storedat a second storage cluster. For example, a different storage clusterfrom the storage cluster that stored the full copy of the data in action804 stores a portion of the data. In an action 808, the remainingcomplementary portion of the data is stored at a third storage cluster.The remaining complementary portion of the data could be formed bytaking the difference between a full copy of the data and the portion ofthe data that is stored in the action 806. In some embodiments thiscould be accomplished by sending alternating segments or other portionsof data to each of two storage clusters, while one storage cluster,differing from these two storage clusters, retains a full copy of thedata as a result of performing the action 804.

In a decision action 810, it is determined if there is a disaster. Forexample, there could be a power failure, component failure, systemfailure, or theft, at one of the storage clusters. If there is adisaster, flow proceeds to the action 814, in order to initiaterecovery. If there is no disaster, flow proceeds to the action 812 inorder to change data destinations in the storage grid. For example, thenext incoming data could be routed to one of the storage clusters thatis different than the storage cluster to which the full copy of theprevious data was written. Rotating the sequences of receiving andstoring data may be accomplished through a random selection, or datacould be routed to the nearest one of the storage clusters each time newdata is received for writing, among other techniques. Over time, forwhichever mechanism is employed, the destinations of the full copy andcopy portions are changed so that no single storage cluster has a copyof all of the data that has been received over time at the storage grid.In addition, any two of the storage clusters in combination have atleast a copy of all of the data that has been received over time at thestorage grid.

If there is a disaster then data is recovered by combining data from twoof the three storage clusters in action 814. In some embodiments therecovery is achieved by interleaving the recovered data potions fromalternating storage clusters. Such recovery is possible as a result ofthe storing, in actions 804, 806, 808, and the systematic changing ofdestinations in action 812. In some embodiments, the action ofrecovering data includes recovering a shared secret as described abovewith reference to FIG. 7, and decrypting data via application of therecovered shared secret to decrypt keys.

The methods described herein may be performed with a digital processingsystem, such as a conventional, general-purpose computer system. Specialpurpose computers, which are designed or programmed to perform only onefunction may be used in the alternative. FIG. 9 is an illustrationshowing an exemplary computing device which may implement theembodiments described herein. The computing device of FIG. 9 may be usedto perform embodiments of the functionality for disaster recovery inaccordance with some embodiments. The computing device includes acentral processing unit (CPU) 901, which is coupled through a bus 905 toa memory 903, and mass storage device 907. Mass storage device 907represents a persistent data storage device such as a disc drive, whichmay be local or remote in some embodiments. The mass storage device 907could implement a backup storage, in some embodiments. Memory 903 mayinclude read only memory, random access memory, etc. Applicationsresident on the computing device may be stored on or accessed via acomputer readable medium such as memory 903 or mass storage device 907in some embodiments. Applications may also be in the form of modulatedelectronic signals modulated accessed via a network modem or othernetwork interface of the computing device. It should be appreciated thatCPU 901 may be embodied in a general-purpose processor, a specialpurpose processor, or a specially programmed logic device in someembodiments.

Display 911 is in communication with CPU 901, memory 903, and massstorage device 907, through bus 905. Display 911 is configured todisplay any visualization tools or reports associated with the systemdescribed herein. Input/output device 709 is coupled to bus 905 in orderto communicate information in command selections to CPU 901. It shouldbe appreciated that data to and from external devices may becommunicated through the input/output device 909. CPU 901 can be definedto execute the functionality described herein to enable thefunctionality described with reference to FIGS. 1-8. The code embodyingthis functionality may be stored within memory 903 or mass storagedevice 907 for execution by a processor such as CPU 901 in someembodiments. The operating system on the computing device may beMS-WINDOWS™, UNIX™, LINUX™, iOS™, CentOS™, Android™, Redhat Linux™,z/OS™, or other known operating systems. It should be appreciated thatthe embodiments described herein may be integrated with virtualizedcomputing system also.

Detailed illustrative embodiments are disclosed herein. However,specific functional details disclosed herein are merely representativefor purposes of describing embodiments. Embodiments may, however, beembodied in many alternate forms and should not be construed as limitedto only the embodiments set forth herein.

It should be understood that although the terms first, second, etc. maybe used herein to describe various steps or calculations, these steps orcalculations should not be limited by these terms. These terms are onlyused to distinguish one step or calculation from another. For example, afirst calculation could be termed a second calculation, and, similarly,a second step could be termed a first step, without departing from thescope of this disclosure. As used herein, the term “and/or” and the “/”symbol includes any and all combinations of one or more of theassociated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes”, and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Therefore, the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that theembodiments might employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing. Any of the operations describedherein that form part of the embodiments are useful machine operations.The embodiments also relate to a device or an apparatus for performingthese operations. The apparatus can be specially constructed for therequired purpose, or the apparatus can be a general-purpose computerselectively activated or configured by a computer program stored in thecomputer. In particular, various general-purpose machines can be usedwith computer programs written in accordance with the teachings herein,or it may be more convenient to construct a more specialized apparatusto perform the required operations.

A module, an application, a layer, an agent or other method-operableentity could be implemented as hardware, firmware, or a processorexecuting software, or combinations thereof. It should be appreciatedthat, where a software-based embodiment is disclosed herein, thesoftware can be embodied in a physical machine such as a controller. Forexample, a controller could include a first module and a second module.A controller could be configured to perform various actions, e.g., of amethod, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on anon-transitory computer readable medium. The computer readable medium isany data storage device that can store data, which can be thereafterread by a computer system. Examples of the computer readable mediuminclude hard drives, network attached storage (NAS), read-only memory,random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and otheroptical and non-optical data storage devices. The computer readablemedium can also be distributed over a network coupled computer system sothat the computer readable code is stored and executed in a distributedfashion. Embodiments described herein may be practiced with variouscomputer system configurations including hand-held devices, tablets,microprocessor systems, microprocessor-based or programmable consumerelectronics, minicomputers, mainframe computers and the like. Theembodiments can also be practiced in distributed computing environmentswhere tasks are performed by remote processing devices that are linkedthrough a wire-based or wireless network.

Although the method operations were described in a specific order, itshould be understood that other operations may be performed in betweendescribed operations, described operations may be adjusted so that theyoccur at slightly different times or the described operations may bedistributed in a system which allows the occurrence of the processingoperations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods andmechanisms described herein may form part of a cloud-computingenvironment. In such embodiments, resources may be provided over theInternet as services according to one or more various models. Suchmodels may include Infrastructure as a Service (IaaS), Platform as aService (PaaS), and Software as a Service (SaaS). In IaaS, computerinfrastructure is delivered as a service. In such a case, the computingequipment is generally owned and operated by the service provider. Inthe PaaS model, software tools and underlying equipment used bydevelopers to develop software solutions may be provided as a serviceand hosted by the service provider. SaaS typically includes a serviceprovider licensing software as a service on demand. The service providermay host the software, or may deploy the software to a customer for agiven period of time. Numerous combinations of the above models arepossible and are contemplated.

Various units, circuits, or other components may be described or claimedas “configured to” perform a task or tasks. In such contexts, the phrase“configured to” is used to connote structure by indicating that theunits/circuits/components include structure (e.g., circuitry) thatperforms the task or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. 112, sixth paragraph, for that unit/circuit/component.Additionally, “configured to” can include generic structure (e.g.,generic circuitry) that is manipulated by software and/or firmware(e.g., an FPGA or a general-purpose processor executing software) tooperate in manner that is capable of performing the task(s) at issue.“Configured to” may also include adapting a manufacturing process (e.g.,a semiconductor fabrication facility) to fabricate devices (e.g.,integrated circuits) that are adapted to implement or perform one ormore tasks.

The foregoing description, for the purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the embodiments and its practical applications, to therebyenable others skilled in the art to best utilize the embodiments andvarious modifications as may be suited to the particular usecontemplated. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

What is claimed is:
 1. A method of storing data, comprising: receivingdata at one storage cluster of a storage grid, the storage gridcomprising multiple storage cluster; storing the data at the firststorage cluster of the storage grid; storing a portion of the data atthe second storage cluster of the storage grid; storing a remainingportion of the data at the third storage cluster of the storage grid;and repeating the receiving and each storing operation with a seconddata, such that no one storage cluster of the storage grid has a fullcopy of the data and a full copy of the second data, wherein at leastone method operation is executed by a processor.
 2. The method of claim1, further comprising: changing data destinations among the storageclusters of the storage grid and wherein each combination of two storageclusters of the storage grid has at least the full copy of the data andthe full copy of the second data.
 3. The method of claim 1, furthercomprising: splitting the data into the portion and the remainingportion, wherein the splitting is performed by one of the storageclusters of the storage grid or a network coupled to each of the storageclusters of the storage grid.
 4. The method of claim 1, wherein the dataincludes a first segment of data and a second segment of data, theportion of the data includes the first segment of data, and theremaining portion of the data includes the second segment of data. 5.The method of claim 1, wherein storing a portion of the data at thesecond storage cluster and storing a remaining portion of the data atthe third storage cluster includes writing alternating segments of datato the second storage cluster and the third storage cluster.
 6. Themethod of claim 1, further comprising: interleaving the portion of thedata and the remaining portion of the data so as to recover a copy ofthe data, responsive to a failure of the first storage cluster of thestorage grid.
 7. The method of claim 1, further comprising: encryptingcontents of each of the first storage, the second storage and the thirdstorage, via a shared secret; and storing a first share of the sharedsecret at the first storage, a second share of the shared secret at thesecond storage, and a third share of the shared secret at the thirdstorage, such that any two of the first share, the second share, and thethird share suffice for decrypting the contents of any of the firststorage, the second storage, and the third storage.
 8. A storage grid,comprising: a first storage cluster, a second storage cluster, and athird storage cluster; and each of the first storage cluster, the secondstorage cluster and the third storage cluster is configured to store anamount of data ranging from a portion of a copy of the data to a fullcopy of the data, for each of at least a first data, a second data and athird data, such that: the first data has a full copy of the first datawritten to the first storage cluster, a partial copy of the first datawritten to the second storage cluster, and a difference between the fullcopy of the first data and the partial copy of the first data written tothe third storage cluster; the second data has a full copy of the seconddata written to the second storage cluster, a partial copy of the seconddata written to the third storage cluster, and a difference between thefull copy of the second data and the partial copy of the second datawritten to the first storage cluster; and the third data has a full copyof the third data written to the third storage cluster, a partial copyof the third data written to the first storage cluster, and a differencebetween the full copy of the third data and the partial copy of thethird data written to the second storage cluster.
 9. The storage grid ofclaim 8, wherein: no one of the first storage cluster, the secondstorage cluster, or the third storage cluster, has a full copy of eachof the first data, a full copy of the second data and a full copy of thethird data; and each two of the first storage cluster, the secondstorage cluster, or the third storage cluster, has at least the fullcopy of each of the first data, the full copy of the second data or thefull copy of the third data.
 10. The storage group of claim 8, furtherconfigured so that in the event of a failure of the first storagecluster, the first data can be recovered by interleaving the partialcopy of the first data, from the second storage cluster and thedifference between the full copy of the first data and the partial copyof the first data, from the third storage cluster, the interleaving at agranularity of a segment.
 11. The storage grid of claim 8, furthercomprising: each of the first storage cluster, the second storagecluster, and the third storage cluster including flash.
 12. The storagegrid of claim 8, further comprising: the first storage cluster, thesecond storage cluster, and the third storage cluster configured tocouple to each other via a network and wherein each of the first storagecluster, the second storage cluster, and the third storage cluster havedifferent storage capacities.
 13. The storage grid of claim 8, furthercomprising: a secret generation unit, configured to generate a sharedsecret applicable to encrypting keys; a share generation unit,configured to generate shares of the shared secret; and each of thefirst storage cluster, the second storage cluster and the third storagecluster configured to store one of the shares of the shared secret. 14.The storage grid of claim 8, further comprising: each of the firststorage cluster, the second storage cluster and the third storagecluster includes a plurality of storage units with solid-state memory.15. A storage grid comprising: a first storage cluster, a second storagecluster, and a third storage cluster; the first storage clusterconfigured to receive a first data, write the first data into the firststorage cluster, send a portion of a copy of the first data to thesecond storage cluster, and send a remaining portion of the copy of thefirst data to the third storage cluster; the second storage clusterconfigured to receive a second data, write the second data into thesecond storage cluster, send a portion of a copy of the second data tothe third storage cluster, and send a remaining portion of the copy ofthe second data to the first storage cluster; and the third storagecluster configured to receive a third data, write the data into thethird storage cluster, send a portion of a copy of the third data to thefirst storage cluster, and send a remaining portion of the copy of thethird data to the second storage cluster.
 16. The storage grid of claim15, wherein: the first storage cluster lacks all of the first data, thesecond data and the third data; the second storage cluster lacks all ofthe first data, the second data and the third data; the third storagecluster lacks all of the first data, the second data and the third data;and wherein any combination of two clusters of the first storagecluster, the second storage cluster, and the third storage cluster canrecover the first data, the second data and the third data.
 17. Thestorage grid of claim 15, wherein the first storage cluster isconfigured to send the copy of the first data and the remaining portionof the copy of the first data as alternating segments of data to thethird storage cluster and the second storage cluster.
 18. The storagegrid of claim 15, further comprising: at least one processor configuredto generate a shared secret and shares of the shared secret; each of thefirst storage cluster, the second storage cluster, and the third storagecluster configured to store at least one of the shares of the sharedsecret, wherein shares of the shared secret from two of the firststorage cluster, the second storage cluster, and the third storagecluster are applicable to decrypt data on any one of the first storagecluster, the second storage cluster, or the third storage cluster. 19.The storage grid of claim 15, wherein the first data, the second dataand the third data is portioned by one of the storage clusters of thestorage grid or a network coupled to each of the storage clusters of thestorage grid.
 20. The storage grid of claim 15, further comprising: thefirst storage cluster and the second storage cluster configured torecover the third data by combining the portion of the copy of the thirddata from the first storage cluster and the remaining portion of thecopy of the third data from the second storage cluster; the secondstorage cluster and the third storage cluster configured to recover thefirst data by combining the portion of the copy of the first data fromthe second storage cluster and the remaining portion of the copy of thefirst data from the third storage cluster; and the third storage clusterand the first storage cluster configured to recover the second data bycombining the portion of the copy of the second data from the thirdstorage cluster and the remaining portion of the copy of the second datafrom the first storage cluster.